Our condo association is considering replacing the 3.5 gallon toilets with 1.6 gallon ones. The water district has a deal that costs only $30 for each toilet, but they offer only 4 models. I was wondering which one is the best.

The condos are 2 story with an upper unit and lower unit, built around 1979 and we're in the San Diego area where the water is quite hard.